1. Field of the Invention
This invention relates to pneumatic valves, and more particularly to lightweight pneumatic valves capable of withstanding the hostile environment generated from solid propellant or other propellants, such as those used in rocket or missile applications.
2. Description of the Related Art
When a missile or other projectile is launched, it is sometimes desired that it steer itself, or provide for its own guidance. A projectile's ability to guide itself can be accomplished by the redirection of the projectile's propellant output, especially for missiles. While valves are sometimes used to redirect propellant thrust, they are subject to certain drawbacks under certain circumstances.
Pneumatic valves for missile applications should be lightweight yet capable of withstanding the environment and effects of hot gasses produced from the missile's engine, which may be a solid rocket type motor, which is also known as a gas generator. A gas generator can generate a gas at temperatures of up to five thousand degrees Fahrenheit (5000° F.). Some valves need not necessarily be capable of withstanding these temperature environments for long periods of time, as the valves may only be required to handle hot gas for short duty cycles.
High temperature divert and attitude control valves for missiles, spacecraft, and other craft may use poppet and piston ring valve elements to function. These attitude control valves have low friction and wear-resistant sliding surfaces in order to function properly for extended periods of time. Linkage and wear problems can exist with high temperature composite valve structures. These problems may relate to material porosity, erosive effects of propellant gasses, and the rapid wear of sliding and contact surfaces of pistons, cylinders, and rings. For these reasons, refractory metals have been used in missile applications.
Feasibility limitations exist with the use of refractory metal valves due to material and manufacturing process restrictions, the high weight density of such materials, and the high unit cost of such materials. It is challenging to develop other coatings and processes for other lighter materials that are capable of withstanding transient thermal expansion effects due to the dramatic change in temperature (ambient temperature to propellant gas temperature).
In addition to the difficulties posed by valves, solid fuel missiles in general with diameters of less than roughly 30 inches have had to depend upon fins to guide the missile. Larger missiles and rockets have used thrust diversion valves in place of fins for guidance. However, conventional thrust valves are of the size and weight that would make them impractical to use for guidance in place of fins on such smaller vehicles having solid fuel and associated high temperature operating environments. This is especially so in the area of solid fueled tactical missiles, which may have a diameter of 10 inches or less.